1. Field of the Invention
The present invention relates to a protective structure for the exterior surface of boats and, more particularly, to a damage resistant impact absorbing structure for use on towboats or tugboats.
2. Description of Prior Art
River towboats or tugboats typically include bumpers comprising padded pusher knees formed of upright beams located on the front of the towboat for engaging and pushing barges. The bumpers generally include solid rubber members molded to a heavy steel backing plate. The rubber is typically two inches thick and the steel backing plate may be from one-quarter inch to one inch thick, depending on the requirements for the towboat.
The typical rubber compound is formed of either a natural rubber base with added fillers and carbon black producing a finished product of 60 Shore A hardness, or a similar hardness from an EPDM rubber compound. The metal plates of the bumpers are welded in place on the pusher knees to protect the towboat at locations where it will contact a barge.
Prior art solid rubber bumper constructions have several inherent problems. One problem associated with the prior bumpers relates to the inability of the bumper to resist shearing forces. Specifically, although the rubber compounds for the bumper are formulated to be relatively tough and resistant to abrasion and tearing, the extreme forces involved in shoving and positioning barges are often greater than the rubber is capable of withstanding. Accordingly, sideways or shearing forces may cause the rubber to be gouged or ripped from the steel backing plate if the bumper engages a barge or dock surface at an angle instead of engaging in direction that is generally perpendicular to the backing plate.
Additionally, rubber does not have naturally a slick or slippery surface characteristics, even when wet, such that when engaging a barge, the force of engagement between the towboat and barge will negate any lubricating effect the water may have between the surfaces. In some cases, the bumper may even become stuck to the barge. Further, various factors may affect the relative position between the towboat and the barge including changing winds and river currents, changes in the fuel load of the towboat, and a change in the number of barges being pushed, requiring repositioning of the rubber of the bumper relative to the barge. The described rubber bumper construction is not well suited to such changing conditions which alter the position of the towboat relative to the barge, in that the changing conditions subject the rubber bumper to shearing forces which tend to damage the bumper.
The current design of bumpers is also relatively heavy and difficult to handle in that a typical bumper member may comprise a one foot-by-three foot three-quarter inch plate having a two inch rubber molded element. This bumper construction, which may weigh over 120 pounds, is welded directly to the contact areas of the towboat. The heavy plate used for the bumper spans any dents and depressions in the supporting structure, i.e., the pusher knees, of the towboat.
There is a need for towboat bumper which is lightweight and durable to accommodate compressive and shearing forces applied against the bumper, and to resist gouging of the bumper surface.